The global energy crisis and anthropogenic global warming have necessitated development of alternate energy sources to curb dependence on fossil fuels. Nuclear energy provides one possible route to alleviate these issues with next generation nuclear reactors and fuels. In this regard, uranium nitride [U≡N]x has arisen as a promising alternative to traditional mixed oxide-fuels, with advantages such as a higher melting point and enhanced thermal conductivity. Unlike the widely studied uranyl ion [O═U═O]2+, very little is known about the U≡N linkage or its chemical behavior and reactivity. A thorough understanding of the physicochemical properties of the U≡N moiety is critical for predicting the long-term behavior of the ceramic nuclear fuel [U≡N]x. The properties of extended ceramic materials are challenging to study, and as such molecular model systems are ideal for the controlled study of this bond fragment. Uranium nitrides are rare, and the few known systems have all been generated through oxidation of reduced uranium centers with either dinitrogen or azide sources. The nitride fragments in these complexes either form bridging linkages between uranium centers or coordinate to Lewis acids, namely B(C6F5)3. These interactions quench any other potential reactivity of the U≡N bond, making the generation of a terminal uranium nitride complex an important goal. A need exists, therefore, for the ability to generate a discrete molecular terminal uranium nitride, which would allow for the study of fundamental reactivity of the isolated U≡N fragment and could shed light on the behavior and properties of bulk [U≡N]x under life-cycle conditions from fuel-element formulation to recovery/reprocessing.
By far the most effective route to access nitride species is through photochemical extrusion of N2 from metal azide complexes (M-N3). For example, the photolysis of Fe azide complexes has been successfully utilized to generate terminal Fe nitrides. However, prior to this work, this reaction has not proven successful for analogous uranium complexes.